分子筛膜论文：氧化铝中空纤维上silicalite-1分子筛膜的合成.doc

分子筛膜论文：氧化铝中空纤维上silicalite-1分子筛膜的合成【中文摘要】分子筛膜由于其规则的孔道结构和吸附性能,能够应用于气体及液体混合物的分离,并且具有较强的机械强度、化学稳定性和热稳定性。Silicalite-1分子筛膜的分子筛骨架中不含有铝,具有较强的表面疏水性,可特别应用于有机物/水溶液中有机物的回收或浓缩。如将其应用于生物发酵制备燃料乙醇的过程中,可以不断地移走产物乙醇,促进反应持续进行,从而提高燃料乙醇的生产效率。目前合成silicalite-1分子筛膜所用的载体几乎都是片状或者管状载体,这类载体的共同点就是壁较厚,增加了分离过程中物质的传质阻力,降低了膜的渗透通量,限制了工业应用。本论文提出使用壁较薄(-150m)及装填密度大(1000m2/m3)的-Al2O3中空纤维为载体,采用二次水热合成法合成了silicalite-1分子筛膜,对合成方法进行优化,制备了性能良好的分子筛膜。将合成的silicalite-1分子筛膜应用在渗透汽化分离乙醇/水混合物体系中,得到了较好的乙醇/水分离效果。研究内容和实验结果如下：研究了合成液中不同TPAOH含量及晶种液浓度对silicalite-1分子筛膜的影响,结果发现随着TPAOH含量的降低,膜的分离因子有所增加,但是当TPAOH含量太低时(x0.12),膜表面不致密,表面晶体呈片状结构；TPAOH含量太高时(x0.32),膜表面相对较为致密,但是EDX证明此时氧化铝载体的溶出较为严重,降低了膜表面的疏水性,从而导致了膜渗透汽化性能的降低。当所用晶种液的浓度很低时,即使合成液中的TPAOH浓度在适当的范围内,由于晶种不能够将载体完全覆盖,在水热合成的过程中,载体同样有溶出的可能；而晶种液的浓度太高,载体表面会形成较厚的晶种层,晶化后膜层和载体之间仍会有一层疏松的晶种层,导致高温焙烧过程中膜表面缺陷和裂缝的产生,从而降低膜的分离性能。当合成液中TPAOH含量x=0.17-0.22,晶种液浓度为5wt.%时,175、12 h合成的silicalite-1分子筛膜对60、3wt.%和75、5wt.%乙醇/水溶液的通量和分离因子分别达到了2.95 kgm-2h-1、66和5.40 kgm-2h-1、54。研究还发现silicalite-1分子筛膜的渗透通量与所用中空纤维载体的孔隙率呈线性关系,69%孔隙率的-Al2O3中空纤维载体上合成的silicalite-1分子筛膜对60、3wt.%乙醇/水溶液的渗透通量可达4.74 kgm-2h-1,远高于文献报道值。为了减少TPAOH浓度对载体溶出的影响和缩短水热合成的时间,本研究还采用先后使用合成液TPAOH:TEOS:H2O=0.17:1:165和TPAOH:TEOS:H2O=0.64:1:165的两步法合成silicalite-1分子筛膜。通过与短时间(2h或4h)内一步法合成的silicalite-1分子筛膜相比,发现短时间两步法可以明显提高膜的分离性能。随着第二步晶化时间的延长,分子筛膜分离性能显著提高,当第二步晶化时间从2h延长到4h,分子膜的分离因子从20多增加到了40以上。第二步晶化时间太长,膜表面有大量晶体的堆积,会对膜的分离性能有一定影响。采用动态旋转法和降低模板剂(TPA+)含量可以明显减少膜表面晶体的堆积。【英文摘要】Zeolite membranes can be used in the separation of gas and liquid mixtures due to their unique pore structures, adsorption properties, strong mechanical strength, chemical stability and thermal stability. Pure silica MFI (Silicalite-1) zeolite membrane with hydrophobicity, can be applied to the recovery or concentration of organic from organic/water mixtures. The ethanol can be continuously removed from the fermentation broth using silicalite-1 membrane in preparing bioethanol from fermentation process, increasing the conversion rate and the overall production efficiency.At present, most membranes reported in literatures were synthesized on flat plates or large diameter tubular supports. The thick wall of the support leads to high resistance of the permeate transport through the support and the reduction of the flux of zeolite membrane, and thus limits its industrial applications. In this paper, silicalite-1 membranes are synthesized by the secondary (seeded) growth method on-Al2O3 hollow fiber supports with thinner wall thickness (150m) and larger loading density (1000 m2/m3). Separation performance measurement of zeolite membranes obtained is carried out in a laboratory scale setup for the pervaporation experiments of ethanol/water mixtures. The main experimental results and conclusions are summarized as follows:Influences of the content of the structure-directing agent (SDA, e.g. TPAOH) in the synthesis solution and the seed suspension concentration are investigated. It is found that high TPAOH content may lead to aluminum leaching from the alumina support seriously and caused the membrane less hydrophobic; low TPAOH content may lead to non-continuous zeolite layer, leading to poor separation performance. A continuous and dense zeolite seed layer is necessary to obtain the silicalite-1 membrane with high separation performance. Weak intergrowth can be found in the silicalite-1 layer and support leaching is serious due to the poor continuity of the seed layer for low seed concentration. However, too thick seed layer may cause peeling and cracking of the membrane and thus decrease the separation performance. The membrane prepared from the synthesis solution molar composition TPAOH:TEOS: H2O= 0.17:1:165 at 175for 12 and the seed suspension of 5 wt.% concentration showed the flux of 2.95 kgm-2h-1 and the separation factor of 66 for 3 wt.% ethanol feed at 60, and 5.40 kgm-2h-1 and 54 for 5 wt.% ethanol feed at 75, respectively. A linear relationship between the flux of silicalite-1 membranes and the support porosity was observed. The silicalite-1 zeolite membrane synthesized on the-Al2O3 hollow fiber with the porosity of 69% showed the flux of 4.74 kgm-2h-1 for 3 wt.% ethanol feed at 60, which is the highest flux compared with data reported in literatures.The silicalite-1 zeolite membrane is also prepared by a two-step method from the synthesis solution molar composition TPAOH:TEOS:H2O= 0.17:1:165 and TPAOH: TEOS:H2O= 0.64:1:165. The two-step method can significantly improve the separation performance compared with the one-step method for a short crystallization time (2 h or 4 h). The separation performance of membrane increased significantly with increasing the second-step crystallization time, when the crystallization time extended from 2 h to 4 h, the separation factor increased from 20 to more than 40. However, longer second-step crystallization time leaded to a large number of extra crystals on the membrane surface, affecting the membrane performance. Smooth zeolite membrane surfaces were obtained by dynamic rotation method and reducing the template (TPA+) content.【关键词】分子筛膜 silicalite-1 中空纤维 渗透汽化 高通量【英文关键词】Zeolite membrane Silicalite-1 Hollow fiber Pervaporation High flux【目录】氧化铝中空纤维上silicalite-1分子筛膜的合成致谢5-6摘要6-8Abstract8-9目录10-13第1章 文献综述13-361.1 膜分离过程简介13-141.2 沸石分子筛膜概述14-151.2.1 沸石分子筛141.2.2 沸石分子筛膜14-151.3 MFI分子筛膜15-331.3.1 MFI分子筛膜的合成方法15-191.3.1.1 水热合成法16-171.3.1.2 微波合成法17-181.3.1.3 气相转移法181.3.1.4 堵孔法18-191.3.2 MFI分子筛膜的表征19-221.3.2.1 结构表征19-211.3.2.2 分离性能表征21-221.3.3 合成MFI分子筛膜的影响因素22-261.3.3.1 载体的影响23-241.3.3.2 晶种及晶种层的影响24-251.3.3.3 水热合成条件的影响25-261.3.3.4 合成液的影响261.3.4 MFI分子筛膜的缺陷和修饰26-281.3.5 MFI分子筛膜的应用28-321.3.5.1 MFI分子筛膜在分离方面的应用28-311.3.5.2 MFI分子筛膜在膜催化反应中的应用31-321.3.5.3 MFI分子筛膜在其他方面的应用321.3.6 高通量silicalite-1分子筛膜的研究现状32-331.4 本课题的研究背景和方案33-361.4.1 研究背景33-341.4.2 研究方案34-36第2章 实验部分36-422.1 实验所用试剂及材料36-372.2 Silicalite-1分子筛膜的制备37-392.2.1 Silicalite-1纳米晶种的制备372.2.2 晶种层的制备37-382.2.3 Silicalite-1分子筛膜的制备382.2.4 Silicalite-1分子筛膜的活化38-392.3 Silicalite-1分子筛膜的表征39-422.3.1